U.S. patent number 6,671,376 [Application Number 09/372,145] was granted by the patent office on 2003-12-30 for video scramble/descramble apparatus.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Shinichiro Koto, Tadaaki Masuda.
United States Patent |
6,671,376 |
Koto , et al. |
December 30, 2003 |
Video scramble/descramble apparatus
Abstract
A video scramble apparatus has a scrambler for scrambling an
input video signal, and a video encoder for performing interframe
predictive coding of the video signal after scrambling, and the
scrambler selects a frame, which is not used as a reference frame
for interframe prediction in the video encoder, from the input
video signal, and scrambles the frame by pixel replacing in units
of slices within a predetermined vertical range or pixel replacing
in units of n consecutive macroblocks within a predetermined
horizontal range.
Inventors: |
Koto; Shinichiro (Kawasaki,
JP), Masuda; Tadaaki (Tokyo, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
|
Family
ID: |
16870469 |
Appl.
No.: |
09/372,145 |
Filed: |
August 11, 1999 |
Foreign Application Priority Data
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Aug 12, 1998 [JP] |
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10-228053 |
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Current U.S.
Class: |
380/210;
348/394.1; 348/E7.056; 382/236; 382/238; 713/176 |
Current CPC
Class: |
G06T
9/004 (20130101); H04N 7/1675 (20130101); H04N
21/2347 (20130101); H04N 21/4405 (20130101); H04N
21/44055 (20130101); H04N 21/8358 (20130101) |
Current International
Class: |
G06T
9/00 (20060101); H04N 7/167 (20060101); H04N
007/167 (); H04N 007/12 (); H04N 011/02 (); H04N
011/04 (); H04L 009/00 () |
Field of
Search: |
;380/217,216,214,210
;713/176 ;382/238,236 ;348/394.01 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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9-298735 |
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Nov 1997 |
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JP |
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10-13827 |
|
Jan 1998 |
|
JP |
|
10-13828 |
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Jan 1998 |
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JP |
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Primary Examiner: Barron; Gilberto
Assistant Examiner: Stulberger; Cas
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, P.C.
Claims
What is claimed is:
1. A video scramble apparatus comprising: a scramble unit which
scrambles a video signal; and a coding unit which subjects the
video signal scrambled by said scramble unit to an inter-picture
predictive coding, wherein said scramble unit selects from the
video signal a picture unused as a reference picture for
inter-picture prediction in said coding unit, and replaces slices
of the selected picture in units of m slices which are consecutive
in a vertical direction in the picture.
2. The video scramble apparatus according to claim 1, which
comprises a scramble pattern generator which generates a scramble
pattern for scrambling the video signal in said scramble unit, a
descramble key generator which generates descramble key information
representing the scramble pattern, and a multiplexer which
multiplexes the descramble key information to at least one of the
video signal to be coded by said coding unit, the video signal
scrambled by said scrambling unit, the coded video data obtained by
said coding unit, and audio data corresponding to the coded video
data.
3. The video scramble apparatus according to claim 2, wherein the
multiplexer multiplexes a digital water mark signal corresponding
to the descramble key information to at least one of the video
signal to be coded by said coding unit, the video signal scrambled
by said scrambling unit, the coded video data obtained by said
coding unit, and audio data corresponding to the coded video
data.
4. A video scramble apparatus comprising: a coding unit which
subjects a video signal to an inter-picture predictive coding, and
outputs first coded video data; and a scramble unit which scrambles
the first coded video data output from said coding unit, wherein
said scramble unit selects from the first coded video data second
coded video data corresponding to a picture, unused as a reference
picture for inter-picture prediction in said coding unit, and
replaces the selected second coded video data corresponding to
slices of the picture in units of m slices which are consecutive in
a vertical direction in the picture.
5. The video scramble apparatus according to claim 4, which
comprises a scramble pattern generator which generates a scramble
pattern for scrambling the first coded video data in said scramble
unit, a descramble key generator which generates descramble key
information representing the scramble pattern or initial data for
creating the scramble pattern, and a multiplexer which multiplexes
the descramble key information to at least one of the video signal
to be coded by said coding unit, the first coded video data
scrambled by said scrambling unit, the first coded video data
obtained by said coding unit, and audio data corresponding to the
coded video data.
6. The video scramble apparatus according to claim 5, wherein the
multiplexer multiplexes a digital water mark signal corresponding
to the descramble key information to at least one of the video
signal to be coded by said coding unit, the video signal scrambled
by said scrambling unit, the coded video data obtained by said
coding unit, and audio data corresponding to the coded video
data.
7. The video scramble apparatus according to claim 4, wherein said
scramble unit includes a multiplexer which adds an offset to a
vertical component of a motion vector of each of the macroblocks
forming the slices in accordance with the replacement of the coded
video data and multiplexes an added result to the coded video
data.
8. The video scramble apparatus according to claim 7, which
comprises a scramble pattern generator which generates a scramble
pattern for scrambling the first coded video data in said scramble
unit, a descramble key generator which generates descramble key
information representing the scramble pattern or initial data for
creating the scramble pattern, and a multiplexer which multiplexes
the descramble key information to at least one of the video signal
to be coded by said coding unit, the video signal scrambled by said
scrambling unit, the coded video data obtained by said coding unit,
and audio data corresponding to the coded video data.
9. The video scramble apparatus according to claim 8, wherein the
multiplexer multiplexes a digital water mark signal corresponding
to the descramble key information to at least one of the video
signal to be coded by said coding unit, the video signal scrambled
by said scrambling unit, the coded video data obtained by said
coding unit, and audio data corresponding to the coded video
data.
10. A video scramble apparatus comprising: a scramble unit which
scrambles a video signal to generate a scrambled video signal; and
a coding unit which subjects the scrambled video signal to
interframe predictive coding, wherein said scramble unit selects
from the video signal a picture unused as a reference picture for
inter-picture prediction in said coding unit, said scramble unit
dividing macroblocks in a slice of the selected picture in units of
m consecutive macroblocks, dividing the m consecutive macroblocks
in units of n consecutive macroblocks (n<m), and replacing the n
macroblocks in a horizontal direction.
11. The video scramble apparatus according to claim 10, which
comprises a scramble pattern generator which generates a scramble
pattern for scrambling the video signal in said scramble unit, a
descramble key generator which generates descramble key information
representing the scramble pattern or initial data for creating the
scramble pattern, and a multiplexer which multiplexes the
descramble key information to at least one of the video signal to
be coded by said coding unit, the video signal scrambled by said
scrambling unit, the coded video data obtained by said coding unit,
and audio data corresponding to the coded video data.
12. The video scramble apparatus according to claim 11, wherein the
multiplexer multiplexes a digital water mark signal corresponding
to the descramble key information to at least one of the video
signal to be coded by said coding unit, the video signal scrambled
by said scrambling unit, the coded video data obtained by said
coding unit, and audio data corresponding to the coded video
data.
13. A video scramble apparatus comprising: a coding unit which
subjects a video signal to inter-picture predictive coding, and
outputs first coded video data; and a scramble unit which scrambles
the first coded video data output from said coding unit, wherein
said scramble unit selects from the first coded video data second
coded video data corresponding to a frame unused as a reference
picture for inter-picture prediction in said coding unit, dividing
macroblocks in a slice of the frame of the selected second coded
video data in units of m macroblocks, dividing the m macroblocks in
units of n macroblocks (n<m), and replacing the n macroblocks in
a horizontal direction.
14. The video scramble apparatus according to claim 13, which
comprises a scramble pattern generator which generates a scramble
pattern for scrambling the first coded video data in said scramble
section, a descramble key generator which generates descramble key
information representing the scramble pattern or initial data for
creating the scramble pattern, and a multiplexer which multiplexes
the descramble key information to at least one of the video signal
to be coded by said coding unit, the video signal scrambled by said
scrambling section, the coded video data obtained by said coding
unit, and audio data corresponding to the coded video data.
15. The video scramble apparatus according to claim 14, wherein the
multiplexer multiplexes a digital water mark signal corresponding
to the descramble key information to at least one of the video
signal to be coded by said coding unit, the video signal scrambled
by said scrambling unit, the coded video data obtained by said
coding unit, and audio data corresponding to the coded video
data.
16. The video scramble apparatus according to claim 13, wherein
said scramble unit includes a multiplexer which adds an offset to a
horizontal component of a motion vector of each of the macroblocks
forming the slice in accordance with the replacement of the coded
video data and multiplexes an added result to the coded video
data.
17. The video scramble apparatus according to claim 16, which
comprises a scramble pattern generator which generates a scramble
pattern for scrambling the first coded video data in said scramble
section, a descramble key generator which generates descramble key
information representing the scramble pattern or initial data for
creating the scramble pattern, and a multiplexer which multiplexes
the descramble key information to at least one of the video signal
to be coded by said coding unit, the video signal scrambled by said
scrambling section, the coded video data obtained by said coding
unit, and audio data corresponding to the coded video data.
18. The video scramble apparatus according to claim 17, wherein the
multiplexer multiplexes a digital water mark signal corresponding
to the descramble key information to at least one of the video
signal to be coded by said coding unit, the video signal scrambled
by said scrambling unit, the coded video data obtained by said
coding unit, and audio data corresponding to the coded video
data.
19. A video scramble apparatus comprising: a scramble unit which
scrambles a video signal to output a scrambled video signal; and a
coding unit which subjects the scrambled video signal to
inter-picture predictive coding, wherein said scramble unit selects
from the video picture signal a picture unused as a reference
picture for inter-picture prediction in said coding unit, said
scramble unit replacing slices of the selected picture in units of
p slices which are consecutive in a vertical direction in the
picture, and said scramble unit divides the macroblocks in units of
m consecutive macroblocks, divides the m consecutive macroblocks in
units of n consecutive macroblocks (n<m), and replaces the n
consecutive macroblocks.
20. A video scramble apparatus comprising: a coding unit which
subjects a video signal to inter-picture predictive coding, and
outputs first coded video data; and a scramble unit which scrambles
the first coded video data output from said coding unit, wherein
said scramble unit selects from the first coded video data second
coded video data corresponding to a picture unused as a reference
picture for inter-picture prediction in said coding unit, and
replaces the selected second coded video data in units of p slices
of the picture which are consecutive in a vertical direction in the
picture, and said scramble unit divides macroblocks of each of the
slices in units of m macroblocks, divides the m macroblocks in
units of n macroblocks (n<m), and replaces the second coded
video data corresponding to the n macroblocks.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a video scramble/descramble
apparatus corresponding to motion predictive/orthogonal transform
coding of videos.
Various encryption techniques have been studied and developed to
prevent unauthorized duplication and unauthorized access for the
purpose of protecting the copyrights of products containing audio
or video information.
For example, in a DVD (Digital Versatile Disc) using MPEG2 video
coding, reconstruction regions are limited by region codes, and
coded data is encrypted by a CSS (Contents Scrambling System).
As a scramble technique for a baseband video signal, techniques
called line rotation which randomly sets one cut point per line and
replacing the right and left line sections of the cut point and
line permutation for randomly replacing scan lines are known. Line
rotation is used to limit access in cooperation with a billing
system as a scramble technique for pay-per-view programs for
satellite broadcast and CATV (cable television).
For the purpose of preventing unauthorized duplication by consumer
analog video tape recorders, a copy protection technique
(Microvision Corporation) is known. In this technique, AGC signals
or color stripe signals in the vertical blanking interval are
manipulated to disable normal recording of copy-protected tape
contents by the VTRS, although such copy-protected tape contents
can be normally displayed on a TV.
Furthermore, a technique called "digital watermarking"
corresponding to digital contents including audio or video
information is known. Digital watermarking embeds data, which
cannot be visually or aurally perceived, in a baseband signal or
coded data of audio or picture data, or the like. Information to be
hidden by digital watermarking includes, for example, copyright
information, copy generation management information, playback
control information, scramble key information, and the like.
The aforementioned techniques have both merits and demerits. For
example, management using region codes unconditionally allows
playback in designated regions, and data encryption by a CSS or the
like does not inhibit playback using an authorized player. Hence,
the region code or CSS can prevent coded data itself from being
duplicated, but cannot prevent unauthorized duplication of a
decoded video signal. On the other hand, the duplication protection
system for analog VTRs depends on models of VTRs, and cannot always
assure the duplication protection effect. In addition, since only
sync signals are manipulated, resistance against unauthorized
attacks is not always high. Furthermore, hiding of copyright
information by, e.g., digital watermarking does not always
technically limit prevention of unauthorized duplication of a video
signal.
More specifically, in order to prevent unauthorized duplication of
a video signal, more robust copyright protection method for the
video signal itself must be used. However, when a conventional
video scramble technique such as line rotation or the like is used,
if the scrambled video signal is coded by MPEG2 which is used in a
DVD or digital broadcast, the coding efficiency lowers compared to
coding of a non-scrambled picture, thus deteriorating the picture
quality of the reconstructed picture. This is because the
conventional video scramble makes an original video picture hard to
discern by lowering temporal spatial correlation of the picture by
random manipulation of the picture, and is contradictory to motion
predictive/orthogonal transform coding such as MPEG2 or the like,
that improves coding efficiency using the temporal spatial
correlation of a picture.
This point will be described in more detail below.
MPEG2 coding uses correlation of a video signal in the space domain
(intraframe correlation) and correlation in the time domain
(interframe correlation), and compresses the data size by removing
redundancy in both these domains. Motion prediction in units of
blocks anticipates an effect of reducing video signal power using
interframe correlation. To reduce the data size by the DCT
(discrete cosine transform) and variable-length coding in
consideration of correlation between neighboring pixels in a frame
and also quantization with weights depending on frequency in
consideration of the nature of human vision, or to variable-length
code only the difference between DC components of neighboring
blocks anticipate reduction of video signal power using intraframe
correlation.
Furthermore, upon coding motion vector information in units of
macroblocks, the difference between the motion vectors of
neighboring macroblocks is variable-length coded as a motion vector
to be coded in consideration of motion similarity between frames in
association with neighboring macroblocks. In this manner, the
information size to be transmitted can be reduced.
However, in the conventional video scramble technique, correlation
is lowered or video contents are made hard to recognize by random
manipulations for the video signal. When a video signal that has
undergone processes such as conventional line rotation, line
permutation, or the like is coded by MPEG2, interline correlation
in a frame considerably lowers, and a reduction of signal power can
no longer be expected in a combination of DCT and variable-length
coding.
When vertical motion components exist in the time domain, even when
an original video picture has predictive efficiency in motion
prediction in units of macroblocks, the similarity between a
reference picture and picture to be coded lowers as a result of
scrambling, and the predictive efficiency considerably drops. More
specifically, the correlation of a video signal expected in MPEG2
coding considerably lowers, and it consequently becomes hard to
reduce video signal power. In order to achieve coding at a
predetermined bit rate, the number of coded bits must be reduced by
coarse quantization, resulting in drop of image quality of the
decoded picture.
As described above, as robust copyright protection method for a
video signal, a scramble process for a video signal itself is
effective. However, when the conventional video scramble technique
is combined with coding such as MPEG2 that uses temporal spatial
correlation, the coding efficiently suffers, resulting in
deterioration of image quality of the reconstructed picture.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a video
scramble apparatus and video descramble apparatus, which are free
from deterioration of image quality even in coding as a combination
of motion predictive and orthogonal transform like MPEG2
coding.
It is another object of the present invention to provide a video
scramble apparatus which can implement video scramble that can
minimize coding efficiency drop and can maintain high image quality
by selecting a frame which is not used as a reference picture in
interpicture predictive coding, i.e., interfield or interframe
predictive coding and scrambling the selected frame using one or
both of pixel replacing in units of m slices in a predetermined
vertical range or pixel replacing in units of n consecutive
macroblocks within a predetermined horizontal range.
According to the first aspect of the present invention, there is
provided a video scramble apparatus comprising a scramble unit
which scrambles a video signal, and a coding unit which performs
interpicture predictive coding of the video signal scrambled by the
scramble unit, wherein the scramble unit selects a picture, which
is not used as a reference picture for interpicture prediction in
the coding unit, from the video picture signal, and replaces slices
as sets of macroblocks located on identical scan lines in the video
picture signal of the selected picture in units of m slices which
are consecutive in a vertical direction in the picture.
In MPEG2 coding, a picture which is not used as a reference picture
means all B-pictures (bi-directional predictive coded pictures),
I-pictures (interframe coded pictures) which are not referred to
from other frames, and P-pictures (forward predictive coded
pictures) which are not referred to from other frames.
Since the video scramble apparatus implements scrambling by
replacing only a picture which is not used as a reference picture
of interframe predictive coding in units of slices in the vertical
direction, a predictive signal of a coded macroblock can be
extracted from an appropriate position of the reference picture
like in normal coding, thus preventing motion predictive efficiency
drop.
Since in MPEG2 coding intraframe correlation is used only in a
block and only between blocks in a slice, the intraframe
correlation never lowers. Furthermore, upon motion vector coding,
since differences are coded in units of neighboring macroblocks in
a slice except for the head position of the slice, the motion
vector differences become constant irrespective of the
presence/absence of scrambling except for the head position of the
slice, and the number of coded bits of motion vector data can be
prevented from increasing.
In MPEG2 coding, the variable-length coding scheme upon coding
motion vector data is determined based on the maximum values of
horizontal and vertical components of motion vectors in the frame,
and as the maximum values become larger, the code length increases.
Hence, when slices are replaced arbitrarily, the maximum value of
vertical components of motion vectors increases, and the number of
coded bits of motion vector data increases. However, upon replacing
a predetermined number of slices within a group including these
slices, an increase in vertical component of the motion vector can
be suppressed to be equal to or smaller than a predetermined value,
and the number of coded bits of motion vector data can be
minimized. Upon replacing slices, when motion vectors with respect
to a reference picture are detected from macroblocks in the
replaced slice, motion vectors are preferably found by search from
a broad range in the vertical direction in correspondence with an
increase in motion amount corresponding to replacement of
slices.
According to the second aspect of the present invention, there is
provided a video scramble apparatus comprising a coding unit which
performs inter-picture predictive coding of a video signal, and
outputting first coded video data; and a scramble unit which
scrambles the first coded video data output from the coding unit,
wherein the scramble unit selects second coded video data
corresponding to a picture, which is not used as a reference
picture for inter-picture prediction in the coding unit, from the
first coded video data, and replaces the selected second coded
video data corresponding to slices in units of m slices which are
consecutive in a vertical direction in the picture, the slices
being sets of macroblocks located on an identical scan line.
In this manner, in the video scramble apparatus of the second
aspect, after video coding for the input video, e.g., MPEG2 coding,
slices in a frame are replaced on the level of coded data as in the
video scramble apparatus of the first aspect, thus obtaining coded
video data which has undergone scrambling equivalent to that by the
video scramble apparatus of the first aspect. In this case, the
motion vector search range need not be broadened upon scrambling,
and a motion vector search can be made within a normal search
range.
According to the third aspect of the present invention, there is
provided a video scramble apparatus comprising a coding unit which
performs inter-picture predictive coding of a video signal, and
outputting first coded video data; and a scramble unit which
scrambles the first coded video data output from the coding unit,
wherein the scramble unit selects second coded video data
corresponding to a picture, which is not used as a reference
picture for inter-picture prediction in the coding unit, from the
first coded video data, and replaces the selected second coded
video data corresponding to slices in units of m slices which are
consecutive in a vertical direction in the picture, the slices
being sets of macroblocks located on an identical scan line, and
the scramble section includes a multiplexer which adds an offset to
a vertical component of a motion vector of each of the macroblocks
constituting the slices in accordance with the replacement of the
coded video data and multiplexes an added result to the coded video
data.
More specifically, in the video scramble apparatus of the third
aspect, offset addition to the vertical component of a motion
vector of each macroblock is added to the scramble unit in the
video scramble apparatus of the second aspect.
The video scramble apparatus of the third aspect can obtain the
following effects in addition to the same effects as those of the
video scramble apparatus of the second aspect. More specifically,
in combination with replacement of coded data in units of slices,
for only a macroblock such as a first macroblock of each slice,
which is coded without coding the difference between motion
vectors, coded data of that motion vector is replaced by coded data
of a motion vector added with a vertical offset upon replacing
slices. In this manner, video scrambling equivalent to that in the
video scramble apparatus of the first aspect can be implemented by
only processes for coded data obtained by directly using a
conventional video coding system.
According to the fourth aspect of the present invention, there is
provided a video scramble apparatus comprising a scramble unit
which scrambles a video signal, and a coding unit which performs
interframe predictive coding of the video signal scrambled by the
scramble unit, wherein the scramble unit selects a picture, which
is not used as a reference picture for inter-picture prediction in
the coding unit, from the video signal, performs first division of
macroblocks located on an identical scan line in the video signal
of the selected picture in units of m consecutive macroblocks,
performs second division in units of n consecutive macroblocks
(n<m) within the m consecutive macroblocks obtained by the first
division, and replaces macroblocks in units of n consecutive
macroblocks obtained by the second division within the m
consecutive macroblocks obtained by the first division.
When scrambling is to be done by replacing macroblocks in the
horizontal direction in an identical slice in a frame which is not
used as a reference picture, the motion vector values and
difference values between neighboring macroblocks upon replacing
macroblocks become large, as described above, and as a consequence,
the picture quality may often deteriorate due to coding efficiency
drop. Especially, when macroblocks are randomly replaced, the
effect of calculating the difference between the motion vectors of
neighboring macroblocks is lost, and the offset of the motion
vector increases to a value around the horizontal size of the
screen at maximum.
By contrast, the video scramble apparatus according to the fourth
aspect performs first division in units of m macroblocks, which
succeed in the horizontal direction, performs second division for
further dividing each of macroblock groups obtained by the first
division in units of n consecutive macroblocks (m>n), and
replaces macroblocks in units of n macroblocks obtained by the
second division within each macroblock group obtained by the first
division. In this manner, the offset to be added to the horizontal
motion vector of each macroblock upon replacing macroblocks is
limited by the first division size.
As for the difference between horizontal motion vectors of
neighboring macroblocks, the difference normally increases at the
head of the set of macroblocks obtained by the second division, but
does not increase at positions other than the head of the second
division. More specifically, according to the video scramble
apparatus of the fourth aspect, video scrambling can be implemented
by replacement of horizontal macroblock sets without considerable
drop of coding efficiency (deterioration of image quality of the
reconstructed picture) by suppressing an increase in the number of
coded bits of motion vector data in MPEG2 coding.
According to the fifth aspect of the present invention, there is
provided a video scramble apparatus comprising a coding unit which
performs inter-picture predictive coding of a video signal, and
outputting first coded video data, and a scramble unit which
scrambles the first coded video data output from the coding unit,
wherein the scramble unit selects second coded video data
corresponding to a frame, which is not used as a reference picture
for inter-picture prediction in the coding unit, from the coded
video data, performs first division of macroblocks located on an
identical scan line in the selected second coded video data in
units of m macroblocks, performs second division of macroblocks in
units of n macroblocks (n<m) within the m macroblocks obtained
by the first division, and replaces the second coded video data
corresponding to macroblocks in units of n macroblocks obtained by
the second division.
According to the video scramble apparatus of the fifth aspect,
after, for example, MPEG2 coding is done using a video signal
before scrambling as in the video scramble apparatuses of the
second and third aspects, macroblocks are replaced on the level of
coded data, thus obtaining coded video data that has been
scrambled.
According to the sixth aspect of the present invention, there is
provided a video scramble apparatus comprising a coding unit which
performs inter-picture predictive coding of a video signal, and
outputting first coded video data, and a scramble unit which
scrambles the first coded video data output from the coding unit,
wherein the scramble unit selects a picture, which is not used as a
reference picture for inter-picture prediction in the coding unit,
from the video signal, performs first division of macroblocks
located on an identical scan line in the video signal of the
selected picture in units of m consecutive macroblocks, performs
second division in units of n consecutive macroblocks (n<m)
within the m consecutive macroblocks obtained by the first
division, and replaces macroblocks in units of n consecutive
macroblocks obtained by the second division within the m
consecutive macroblocks obtained by the first division, and the
scramble unit includes a multiplexer which adds an offset to a
horizontal component of a motion vector of each of the macroblocks
in accordance with the replacement of the coded video data and
multiplexes an added result to the coded video data.
In the video scramble apparatus according to the sixth aspect,
offset addition to the horizontal component of a motion vector of
each macroblock is added to the scramble unit in the video scramble
apparatus according to the fifth aspect.
The video scramble apparatus according to the sixth aspect can
obtain coded data that has undergone scrambling equivalent to that
of the video scramble apparatus according to the fourth aspect by
only processes for coded data, which is coded by a normal video
coding system.
In a video scramble apparatus according to the seventh aspect of
the present invention, at least one of video scramble apparatuses
according to the first to third aspects is combined with at least
one of video scramble apparatuses according to the fourth to sixth
aspects.
Since replacement of slices in the vertical direction and replacing
in units of n consecutive macroblocks in the horizontal direction
are nearly free from coding efficiency drop, as described above,
they may be combined to implement video scrambling as in the video
scramble apparatus according to the seventh aspect. By combining
these scramble schemes, more robust video scrambling can be
implemented. That is, by increasing the number of scramble schemes
to be combined, resistance against unauthorized attacks can be
strengthened, and an effect of making an original video picture
hard to recognize can be improved as scramble manipulations becomes
more complicated.
By controlling horizontal and vertical scramble patterns or their
combinations according to the present invention, resistance against
unauthorized attacks and the way a picture looks can be controlled
in correspondence with application's requests.
Video data scrambled by the video scramble apparatus of the present
invention is sent to a transmission system. A storage medium may be
used as a transmission system, scrambled video data may be recorded
on that storage medium, and may be descrambled upon playback. A
transmission line such as a terrestrial wave, satellite, cable,
Internet, or the like may be used as a transmission system, and
scrambled video data may be transmitted and descrambled in real
time via such transmission system.
In a video scramble apparatus according to the eighth aspect of the
present invention, the video scramble apparatus according to one of
the first to seventh aspects further comprises a replacing pattern
generator for generating a slice or macroblock replacing pattern
for scrambling in the scramble unit, a descramble key generator for
generating the replacing pattern or initial data for generating the
replacing pattern as a descramble key, and a multiplexer for
multiplexing the descramble key on at least one of video data to be
coded by the coding unit, a video signal scrambled by the scramble
unit, coded video data obtained by the coding unit, and audio data
multiplexed with (or associated with) the encoded video data.
The replacing patterns of slices in the vertical direction and
replacing patterns in units of n consecutive macroblocks in the
horizontal direction may be determined based on random patterns
generated by the scramble apparatus. When the random pattern
itself, a random pattern generator, or its initial value is sent to
an authorized receiver as a key for descrambling (descramble key;
secret key), descrambling can be achieved on the receiving
side.
The descramble key or a part of the descramble key can be sent via
a route different from that of coded video data, e.g., via an IC
card, telephone line, or the like. A part of the descramble key may
be multiplexed on coded video data or audio data associated with
that video data.
There are a case (1) that the descramble key itself is obtained by
a path (IC card, internet and the like) different from that of the
coded video data and a case (2) that in a transmission side, a part
of construction elements of the key data is obtained by a path
different from that of the coded video data and the remainder
thereof is transmitted with being multiplexed with the coded video
data, using the digital water marking, and in a receiver side the
key is reconstructed by combining the part of the key data and the
remainder thereof. In the cases, a part of the descramble key can
be hidden in contents using the aforementioned digital watermarking
technique. A part of the descramble key may be hidden in a video
signal before or after scrambling using digital watermarking.
When the descramble key is hidden in the scrambled video signal,
since descrambling is done after the key is detected, data can be
descrambled without any delay time. When the key is hidden in a
picture signal before scrambling, a key for the next scrambled
picture is extracted from the descrambled picture signal to
descramble that picture. In the former case, descramble key
information disappears by descrambling, and any delay time between
key detection and the descramble process can be minimized.
Conversely, in the latter case, digital watermark information
containing the descramble key remains even after descrambling and,
for example, playback control information can be hidden in the
picture signal together with the descramble key.
Note that the hidden descramble key must be that for a picture
input after that key. These two schemes can be selectively used
depending on applications.
A key for descrambling the scrambled video signal may be hidden in
an audio signal associated with the video signal. Normally, a pair
of video signal and audio signal are strictly synchronously played
back. That is, even when the descramble key for a corresponding
video signal is hidden in an audio signal, their relationship can
be strictly saved, and the video signal can be normally
descrambled.
In this manner, when some data of the descramble key are sent while
being hidden in a video signal or audio signal, even when the
scramble pattern, i.e., the descramble key is varied temporally,
normal descrambling can be done without disturbing the relationship
between the scramble pattern and descramble key. Also, by changing
the key frequently in consecutive video signals, resilience against
unauthorized attacks can be improved.
For example, of the descramble key, data which frequently change
temporally may be hidden in a video or audio signal, and data fixed
in units of, e.g., programs may be sent from a route such as an IC
card, telephone line, or the like. When the descramble key is
hidden using digital watermarking, a key that frequently changes
temporally need not be set using blanking interval information of a
video signal as a video signal or another signal route, and the
interface between devices can be simplified.
A video descramble apparatus according to the present invention
comprises a receiver unit for receiving coded video data coded and
scrambled by a video scramble apparatus of any one the first to
eighth aspects, a decoding unit for decoding the coded video data
received by the receiver unit to obtain a video signal, a
descramble unit for descrambling the video signal obtained by the
decoding unit, and a descramble key extraction unit for extracting
the descramble key from at least one of the coded video data
received by the receiver unit, the video signal obtained by the
decoding unit, the video signal output from the descramble unit,
and audio data included in the coded video data, and the descramble
unit descrambles the video signal obtained by the decoding unit
using the descramble key extracted by the scramble key extraction
unit.
In this manner, in the video scramble apparatus of the present
invention, since a descramble key is detected, encoded video data
is decoded, and the decoded data is descrambled on the basis of the
scramble pattern determined by the detected descramble key to
output a video signal, a normal video signal can be played
back.
Even when an unauthorized receiver decodes coded video data, he or
she can only obtain a scrambled video signal, thus protecting the
copyright of the corresponding contents.
Furthermore, according to the present invention, there is provided
a recording medium that records video data, which is coded and
scrambled by one of the video scramble apparatuses according to the
first to eighth aspects. Since video data coded and scrambled
according to the present invention cannot be normally played back
even if its unauthorized duplication can be made, the copyright can
be protected even on the recording medium.
Additional objects and advantages of the invention will be set
forth in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate presently preferred
embodiments of the invention, and together with the general
description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
FIG. 1 is a block diagram of a video coding/decoding system
according to the first embodiment of the present invention;
FIG. 2 is a block diagram of a video coding/decoding system
according to the second embodiment of the present invention;
FIG. 3 is a block diagram of a video coding/decoding system
according to the third embodiment of the present invention;
FIG. 4 is a block diagram of a video coding/decoding system
according to the fourth embodiment of the present invention;
FIG. 5 is a block diagram of a video coding/decoding system
according to the fifth embodiment of the present invention;
FIG. 6 is a block diagram of a video coding/decoding system
according to the sixth embodiment of the present invention;
FIG. 7 is a block diagram of a scrambler shown in FIGS. 1, 2, and
5;
FIG. 8 is a block diagram of a scrambler shown in FIGS. 3, 4, and
6;
FIG. 9 is a block diagram of a descrambler shown in FIGS. 1 to
6;
FIGS. 10A to 10C are views showing interframe predictive structures
in MPEG2 coding;
FIG. 11 is a view for explaining a method of coding motion vector
data in MPEG2 coding;
FIGS. 12A and 12B are views for explaining a video scramble method
according to the seventh embodiment of the present invention;
FIG. 13 is a view for explaining a video scramble method according
to the eighth embodiment of the present invention;
FIGS. 14A and 14B are views for explaining a video scramble method
according to the ninth embodiment of the present invention;
FIGS. 15A and 15B are views for explaining a video scramble method
according to the 10th embodiment of the present invention; and
FIGS. 16A and 16B are views for explaining a video scramble method
according to the 11th embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiments of the present invention will be
described hereinafter with reference to the drawings.
FIG. 1 shows the arrangement of a video coding/decoding system to
which a video scramble/descramble apparatus according to the first
embodiment of the present invention is applied. This video
coding/decoding system complies with MPEG2 video specifications.
The same applies to all the embodiments to be described
hereinafter.
Referring to FIG. 1, a video coding system 100A comprises a digital
watermark multiplexer 101, first digital watermark detector 102,
scrambler 103, random number generator 104, second digital
watermark detector 106, digital watermark multiplexer 107, and
video encoder 108. On the other hand, a video decoding system 200A
connected to the video coding system 100A via a transmission system
120 comprises a video decoder 201, descrambler 202, second digital
watermark detector 203, and first digital watermark detector 204.
Note that the transmission system 120 may be either of a
broadcast/communication system such as a satellite, terrestrial
wave, or the like, or a storage medium such as a DVD or the
like.
The video coding system 100A will be explained first.
A digital watermark signal 112 generated by the first digital
watermark detector 102 is multiplexed on a video signal (to be
referred to as a video signal hereinafter) 111 input to the video
coding system 100A by the digital watermark multiplexer 101, and
the video signal 111 is then scrambled by the scrambler 103. The
arrangement of the scrambler 103 and its practical scramble method
will be described in detail later.
The digital watermark signal 112 contains copyright information,
reconstruction or playback control information, and the like. When
such information need not be hidden, the digital watermark signal
112 need not be multiplexed on the video signal 111. The scramble
pattern in the scrambler 103 is determined on the basis of scramble
key information 113 generated by the random number generator 104
and video coding information 117 output from the video encoder
108.
The video coding information 117 contains information indicating
one of coding picture types of the respective pictures, i.e.,
frames, that is, I-picture (intraframe coded picture), P-picture
(forward predictive coded picture), and B-picture (bi-directional
predictive coded picture). The scrambler 103 performs a video
scramble process according to the present invention for a frame,
which is not used as a reference picture on the basis of the video
coding information 117.
FIGS. 10A, 10B, and 10C show examples of the interframe predictive
structures in MPEG2 coding. In these figures, the abscissa plots
time, and the predictive structure between neighboring frames is
indicated by an arrow from a reference picture to a picture to be
coded. FIGS. 10A to 10C show different examples of predictive
structures. A hatched frame in FIGS. 10A to 10C indicates a frame
used as a reference picture. In FIG. 10A, since B-frames are not
used as reference pictures, all B-frames are scrambled. In FIG.
10B, since all frames are I-frames, and interframe prediction is
not used, all frames are scrambled. In FIG. 10C, since prediction
using P-frames is not made, all P-frames are scrambled.
A digital watermark signal 115 generated by the second digital
watermark detector 106 is multiplexed on a video signal 114
containing frames scrambled by the scrambler 103 by the digital
watermark multiplexer 107, and a video signal 116 multiplexed with
the digital watermark signal 115 is coded by the video encoder 108.
The digital watermark signal 115 contains information that pertains
to the scramble key information 113 from the random number
generator 104. Coded video data output from the video encoder 108
is output onto the transmission system 120.
The video decoding system 200A will be explained below.
The video decoding system 200A receives the scrambled coded video
data from the transmission system 120, and executes a normal video
decoding process by the video decoder 201. A video signal 211
obtained by this decoding is scrambled. The second digital
watermark detector 203 corresponding to the second digital
watermark detector 106 detects scramble key information 212 from
the scrambled video signal 211, and sends the detected key
information to the descrambler 202.
The descrambler 202 reconstructs a descramble key on the basis of
the scramble key information 212 and externally input second
information 213 that pertains to the scramble key, and descrambles
the video signal 211 output from the video decoder 201. The
arrangement of the descrambler 202 will be described later.
Note that the second information 213 that pertains to the scramble
key information is given to an authorized video coding system or
user, and is hidden in the authorized video coding system or is
given from an IC card or network as needed. In the latter case, the
second information 213 is given in association with a billing
system of, e.g., pay-per-view programs.
A video signal 214 descrambled by the descrambler 202 is output as
an output signal 215 to be output to a video display device or
recording device. When information such as copyright information,
playback control information, or the like is multiplexed as a
digital watermark on the video signal 214, the video signal 214 is
input to the digital watermark detector 204 corresponding to the
first digital watermark detector 102, and digital watermark
information 216 is output. The digital watermark information 216 is
used to specify a copyright holder, or used in video playback
control, video recording control, or the like.
FIG. 2 shows a video coding/decoding system to which video scramble
method and apparatus according to the second embodiment of the
present invention are applied. The same reference numerals in FIG.
2 denotes the same parts as in FIG. 1, and the difference from the
first embodiment will be mainly explained below. In this
embodiment, the multiplexing method of scramble key information 113
in a video coding system 100B is different from the first
embodiment.
That is, in the video coding system 100B of this embodiment,
scramble key information 113 generated by a random number generator
104 is input to a digital watermark detector 102, and is
multiplexed on a video signal 111 before scrambling as a digital
watermark signal 112 by a digital watermark multiplexer 101.
On the other hand, in a video decoding system 200B, a digital
watermark detector 203 detects scramble key information 212 from a
video signal 214 reconstructed via a video decoder 201 and
descrambler 202, and inputs the detected information to a
descrambler 203 together with second information 213 that pertains
to a scramble key.
That is, in the first embodiment shown in FIG. 1, detection of the
scramble key information and descrambling form a feed-forward loop,
and key information that pertains to a scrambled video frame can be
multiplexed on the scrambled picture itself. However, in the second
embodiment shown in FIG. 2, detection of the scramble key
information and descrambling form a feedback loop, and multiplexing
and detection by means of digital watermarking are done in advance
for scramble key information for a following video frame.
In this embodiment, information such as playback control
information or the like, which is not associated with scrambling,
can be multiplexed on a scrambled video signal 114 in addition to
the digital watermark signal 115 generated by the digital watermark
detector 106 in the video coding system 100A. In the video decoding
system 200B, such digital watermark information is detected from a
scrambled video signal 211, decoded by the video decoder 201, by a
digital watermark detector 204, and the scrambled video signal 211
is descrambled by the descrambler 203 later.
As described above, according to this embodiment, digital watermark
information such as playback control information or the like can be
automatically erased by descrambling. On the other hand, in the
first embodiment, since copyright information, playback control
information, or the like is multiplexed as a digital watermark on a
signal before scrambling, that information is saved even after
decoding by the decoder and descrambling. The individual features
of the first embodiments can be selectively used in correspondence
with application requests.
FIG. 3 shows the arrangement of a video coding/decoding system
using video scramble method and apparatus according to the third
embodiment of the present invention.
The same reference numerals denote the same parts as those in FIGS.
1 and 2, and the difference from the first and second embodiments
will be mainly explained below. In this embodiment, in a video
coding system 100C, a digital watermark signal 112 containing,
e.g., copyright information, playback control information, and the
like from a digital watermark detector 102 is multiplexed on an
input video signal 111 by a digital watermark multiplexer 101, and
the video signal multiplexed with the digital watermark signal 112
is coded by a video encoder 108. Coded video data 121 output from
the video encoder 108 is scrambled by a scrambler 103.
More specifically, in the first and second embodiments, the input
video signal 111 is scrambled first, and is then coded, while in
this embodiment, the input video signal 111 is coded by the video
encoder 108 first, and is then scrambled by the scrambler 103.
Scramble key information 113 generated by a random number generator
104 is input to a second digital watermark detector 106, and is
multiplexed as a digital watermark signal 115 on scrambled coded
video data 122 by a digital watermark multiplexer 107.
On the other hand, in a video decoding system 200C, the received,
scrambled coded video data is decoded by a video decoder 201, and a
second digital watermark detector 203 detects scramble key
information 212 from the received coded video data.
A video signal 211 decoded by the video decoder 201 is input to a
descrambler 202 together with the scramble key information 212
detected by the digital watermark detector 203, and second
information 213 that pertains to a scramble key, and is
descrambled. A descrambled video signal 214 is output as an output
signal 215 to be output to a video display device or recording
device, and is input to a first digital watermark detector 204 to
output digital watermark information 216 such as copyright
information, playback control information, or the like.
In this embodiment, although the video coding system 100C scrambles
the coded video data 121, the video decoding system 200C can play
back a picture by descrambling a video signal which is obtained by
decoding the scrambled coded video data without descrambling
it.
In scrambling such as CSS or the like for normal coded data,
descrambling is done before the video decoder, and the picture
obtained by decoding is a normal one. However, according to this
embodiment, since both the coded video data and decoded video
signal are scrambled, the copyrights of both the signals can be
protected.
Furthermore, according to this embodiment, since the scrambler 103
scrambles the coded video data 121 obtained by coding the input
video signal 111 by the video encoder 108, the motion vector search
range need not be broadened upon scrambling, and a motion vector
search can be made within a normal search range. Hence, performance
equivalent to a normal video coding system can be obtained in terms
of motion vector detection.
Since the scrambler 103 scrambles the compressed, coded video data
121, the processing speed can be lowered in accordance with the
compression ratio unlike scrambling for the input video signal 111
in the first and second embodiments.
FIG. 4 shows the arrangement of a video coding/decoding system
which uses a video scramble/descramble apparatus according to the
fourth embodiment of the present invention.
The difference between this embodiment and the third embodiment
shown in FIG. 4 lies in that scramble key information 113 generated
by a random number generator 104 is input to a digital watermark
detector 102, and is multiplexed as a digital watermark signal 112
on an input video signal 111 by a digital watermark multiplexer 101
in a video coding system 100D.
On the other hand, in a video decoding system 200D, a digital
watermark detector 203 detects a descramble key 212 from a video
signal 214, which is obtained by descrambling a video signal 211,
decoded by a video decoder 201, by a descrambler 202, and inputs
the key to the descrambler 202 together with second information 213
that pertains to a scramble key.
FIG. 5 shows the arrangement of a video coding/decoding system
which uses a video scramble/descramble apparatus according to the
fifth embodiment of the present invention.
In this embodiment, in a video coding system 100E, a scrambler 103
scrambles an input video signal 111, a video encoder 108 codes a
scrambled video signal 114, and an audio encoder 132 codes an input
audio signal 141 associated with the input video signal 111. The
coded video data output from the video encoder 108 and coded audio
data output from the audio encoder 132 are multiplexed by a
multiplexer 133, and the multiplexed data is output onto a
transmission system 120.
On the other hand, in a video decoding system 200E, a demultiplexer
231 demultiplexes the coded video and audio data from the received
coded data, and these coded video and audio data are respectively
decoded by a video decoder 201 and audio decoder 232. A decoded
video signal 211 output from the video decoder 201 is descrambled
by a descrambler 202, and a descrambled video signal 215 is output
together with an audio signal 243 decoded by the audio decoder
232.
In the video coding system 100E, a digital watermark signal 112
containing scramble key information 113 for a video signal is
generated by a digital watermark detector 102, and is multiplexed
on the input audio signal 141 associated with the input video
signal 111 by a digital watermark multiplexer 131. In the video
decoding system 200E, a digital watermark detector 204 detects
scramble key information 242 for a video signal, which was
multiplexed by digital watermarking, from the decoded audio signal
241, and that information is input to the descrambler 202 together
with second information 213 that pertains to a scramble key.
FIG. 6 shows the arrangement of a video coding/decoding system
which uses a video scramble/descramble apparatus according to the
sixth embodiment of the present invention.
In this embodiment, the order of a scrambler 103 and video encoder
108 in a video coding system 100F is opposite to that in the fifth
embodiment shown in FIG. 5, and the arrangement of a video decoding
system 200F is the same as that of the video decoding system 200E
shown in FIG. 5.
The arrangement of a scrambler for a video signal in the
embodiments of the present invention will be described below.
FIG. 7 is a block diagram showing an example of the arrangement of
the scrambler 103 shown in FIGS. 1, 2, and 5. The scrambler shown
in FIG. 7 receives a seed 41 for a random number generator, and a
video signal 42, and outputs a scrambled video signal 44 and
descramble key 43. The input video signal 42 is temporarily stored
in a picture memory 38, and a sync signal 45 demultiplexed from the
input video signal 42 by a demultiplexer 37 is input to a scramble
pattern generator 30A.
The scramble pattern generator 30A generates a readout address 47
of the picture memory (RAM) 38 in correspondence with the seed 41
for the random number generator 104. When a video signal is read
out from the picture memory 38 in accordance with the generated
readout address 47, the scrambled video signal 44 is output from
the scrambler 103.
In the scramble pattern generator 30A, the seed 41 is input to a
first random number generator 31, and a descramble key generator 32
generates a descramble key on the basis of a random number
generated by the random number generator 31. The generated
descramble key is input to a second random number generator 34, and
a scramble pattern generator 35 generates a scramble pattern
determined according to a random number generated by the random
number generator 34.
An address generator 36 generates the readout address 47 of the
picture memory 38 on the basis of the scramble pattern from the
scramble pattern generator 35, thus reading out picture data. The
descramble key generated by the descramble key generator 32 is
coded by a key encoder 33, and is output as the descramble key
43.
Assume that the algorithms of the building components of the
scramble pattern generator 30A and the value of the seed 41 for the
first random number generator 31 are not disclosed. Also, of the
building components of the scramble pattern generator 30A, the seed
41 for the first random number generator 31 and the algorithms of
the first random number generator 31 and descramble key generator
32 are inherent to each video coding system and are independently
installed in each video coding system.
On the other hand, assume that the algorithms of the second random
number generator 34, scramble pattern generator 35, and descramble
key encoder 33 are shared between the video coding system and the
corresponding video decoding system and their contents are not
disclosed.
FIG. 8 shows an example of the arrangement of the scrambler 103
shown in FIGS. 3, 4, and 6. The arrangement of a scramble pattern
generator 30B in FIG. 8 is functionally the same as that of the
scramble pattern generator 30A in FIG. 7. Referring to FIG. 8,
coded video data 48 and a seed 41 for a first random number
generator 31 are input, and scrambled coded data 49 and a
descramble key 43 are output from the scrambler 103.
The coded video data 48 is temporarily stored in a memory 51, and
undergoes syntax parsing by a variable length decoder 52. The
variable length decoder 52 outputs a sync signal 61 to the scramble
pattern generator 30B in synchronism with a given position such as
a boundary of a frame or macroblock.
The scramble pattern generator 30B generates a scramble pattern 65
in accordance with the seed 41 for the first random number
generator 31 and in synchronism with the sync signal 61 input from
the variable length decoder 52 as in the scrambler shown in FIG. 7,
thus generating a readout address 47 of the coded video data stored
in the memory 51.
A syntax generator 53 corrects coded data that pertains to a motion
vector of the coded data in accordance with the coded data analyzed
by the variable length decoder 52 and the scramble pattern 65
generated by the scramble pattern generator 30B. More specifically,
motion vector data is corrected by adding an offset to the
horizontal or vertical component of a motion vector in
correspondence with the moving amount of the macroblock position
upon replacing slices or macroblocks in a frame so as to
variable-length code the motion vector again.
A multiplexer 54 multiplexes coded data 64 read out from the
picture memory 51 in accordance with the readout address 47 for
video data, which is generated in correspondence with the scramble
pattern 65, and coded data 63 obtained by correcting some coded
data by the syntax generator 53, and outputs the multiplexed data
as the scrambled coded data 49.
When coded video data obtained by coding a video signal scrambled
by the scrambler shown in FIG. 7, and data obtained by scrambling
coded video data, which is coded without scrambling, by the
scrambler shown in FIG. 8 on the coded data level are decoded and
displayed by the video decoding system, identical scrambled
reconstructed pictures are obtained as long as the same scramble
pattern is used. More specifically, using the scrambler shown in
FIG. 8, processes equivalent to scrambling of an input video signal
before coding can be implemented by scrambling coded video
data.
The arrangement of a descrambler for a video signal in the
embodiments of the present invention will be explained below.
FIG. 9 shows an example of the arrangement of the descrambler 202
shown in FIGS. 1 to 7. This descrambler receives a digital
watermark or an externally input coded scramble key 81 in the video
decoding system, and a decoded video signal 82, and outputs a
descrambled video signal 83. The input video signal 82 is scrambled
one and as such unfit for appreciation. The scrambled input video
signal 82 is temporarily stored in a picture memory 76 as a picture
signal 84 via a demultiplexer 75, and a sync signal 85
demultiplexed from the input video signal 82 by the demultiplexer
75 is input to a scramble pattern reconstruction section 70.
The scramble pattern reconstruction section 70 receives the coded
scramble key 81 together with the sync signal 85. The coded
scramble key 81 is decoded by a key decoder 71. A random number
generator 72 generates a random number in accordance with the
decoded scramble key, and a scramble pattern generator 73
reconstructs a scramble pattern on the basis of this random number.
An address generator 74 calculates the readout address of the
picture memory 76 on the basis of the reconstructed scramble
pattern, and the video signal is read out from the picture memory
76 in accordance with the calculated address, thus outputting a
descrambled video signal 83.
Assume that the algorithms of the key decoder 71, random number
generator 72, and scramble pattern generator 73 in the scramble
pattern reconstruction section 70 of this descrambler are not
disclosed. Also, as these algorithms, the same algorithms as those
in the scrambler are shared.
The method of coding motion vectors used in MPEG2 video coding in
the video encoder 108 in the first to sixth embodiments will be
described below with reference to FIG. 11.
In MPEG2 video coding, the difference between the motion vector of
a macroblock to be coded, and the motion vector of a neighboring
macroblock on the left side of the macroblock to be coded is
calculated, and that difference vector is coded using a
variable-length code. However, (1) at the head position of a slice
and (2) immediately after an intra-macroblock having no vector
information, not the difference vector but the motion vector of the
macroblock to be coded is coded.
Referring to FIG. 11, reference numerals 10, 11, and the like
denote macroblocks in a frame, and the dotted arrows (e.g., an
arrow 15) indicate motion vectors detected in units of macroblocks.
The difference between each of such motion vectors, and the motion
vector of its neighboring macroblock is indicated by a solid arrow
(e.g., an arrow 14), and this value is coded. When motion vectors
between neighboring macroblocks match each other, motion vector
components to be coded are (0, 0). However, since motion vectors 13
and 16 are located at the head positions of slices, and a motion
vector 17 is located immediately after an intra-macroblock,
differences are not calculated for these motion vectors, and the
motion vectors themselves are coded.
The variable-length code of each motion vector is coded by a
combination of a code field having a fixed length in each
macroblock in a frame, and a code field having a variable length in
units of macroblocks in correspondence with the maximum value of
motion vectors in the frame. In either field, the code length
becomes smaller as the motion vector component assumes a smaller
value. That is, the number of coded bits of a motion vector is
determined depending on the maximum value of motion vectors in a
frame, and the degree of correlation between the motion vectors of
neighboring macroblocks.
The video scramble apparatus according to the present invention can
prevent motion compensation predictive efficiency from lowering,
and can avoid coding efficiency drop prevented upon DPCM coding of
the DC components of DCT coefficients and upon variable-length
coding of AC components thereof by scrambling only frames which are
not used as a reference picture, and inhibiting scrambling on
levels smaller than a macroblock as a coding unit. However, the
number of coded bits of a motion vector increases due to an
increase in motion vector size upon replacing slices or macroblocks
or due to an increase in motion vector difference between
neighboring macroblocks. However, according to the video scramble
apparatus of the present invention, an increase in the number of
coded bits of motion vector data can be minimized.
Examples of video scramble methods executed in the scramblers 103
of the first to sixth embodiments will be explained below as the
seventh to 11th embodiments of the present invention. FIGS. 12A to
16B show scramble methods upon replacing slices or a plurality of
macroblocks in a frame according to the present invention.
FIGS. 12A and 12B show a video scramble method according to the
seventh embodiment of the present invention. FIGS. 12A and 12B show
an example of replacing in units of slices in the vertical
direction. Referring to FIGS. 12A and 12B, reference numerals 1, 2,
and 3 denote slices. FIG. 12A shows the slice positions of a frame
before scrambling, and FIG. 12B shows the slice positions of the
frame after scrambling. In the example shown in FIGS. 12A and 12B,
the order of three slices is randomly replaced in units of three
consecutive slices.
As for three slices of screen information in FIGS. 12A and 12B, the
order of slices 1, 2, and 3 is changed to 2, 1, and 3. In FIG. 12A,
the motion vectors of macroblocks at the head positions of the
slices are indicated by arrows. In order to realize the reference
relationship of motion compensation prediction in units of
macroblocks as in FIG. 12B in a scrambled picture shown in FIG.
12A, offsets corresponding to replacement of slices must be added
to the vertical components of motion vectors of the respective
macroblocks. For example, negative offsets corresponding to the
number of lines per slice must be added to the vertical components
of motion vectors in the respective macroblocks of slice 1, and
positive offsets corresponding to the number of lines per slice
must be added to the vertical components of motion vectors in the
respective macroblocks of slice 2.
As for macroblocks which are coded by coding difference vectors
with neighboring macroblocks in the slice, since the offset to be
added to the motion vectors in the slice is constant, no offset
need be added to the difference vectors. That is, the number of
coded bits of motion vector data upon scrambling increases in only
a macroblock located at the head position of each slice and a
macroblock located immediately after an intra-macroblock, and the
increase can be minimized.
Since the number of slices to be replaced is limited to three, an
increase in maximum value of motion vectors can be only the number
of lines corresponding to two slice widths at maximum, and an
increase in the number of coded bits of motion vector data can also
be suppressed. Even in the descrambler, descrambling can be
implemented by only a memory size corresponding to two slices. More
specifically, since the replacing range of slices in the vertical
direction is limited to a predetermined range (three slices in this
case) and replacement is done within this range, any large increase
in the number of coded bits of motion vector can be suppressed
compared to a case wherein slices are randomly replaced in the
entire frame, thus minimizing deterioration of image quality due to
coding efficiency drop. Also, the picture memory size required in
the descrambler can be greatly reduced.
FIG. 13 shows an example of a video scramble method according to
the eighth embodiment of the present invention. FIG. 13 shows an
example wherein replacement is done in the vertical direction using
slice units different from those in FIGS. 12A and 12B. In the
example shown in FIG. 13, the maximum value (four in this case) of
a predetermined number of slices to be replaced is determined, and
slices are randomly replaced in units of slices, the number of
which is equal to or smaller than the maximum value. In FIG. 13,
the slice replacing ranges respectively include three, two, four,
three, and two slices from the upper end in the frame, and slices
are replaced within these ranges. Each slice replacing range is
randomly determined to include a predetermined number or less of
slices. In this manner, the number of scramble patterns can be
increased, and resilience against unauthorized attacks to
scrambling can be strengthened.
FIGS. 14A and 14B show an example of a video scramble method
according to the ninth embodiment of the present invention. FIGS.
14A and 14B exemplify a case wherein scrambling is implemented by
replacing macroblocks within a slice. FIG. 14A shows the macroblock
positions in an original picture frame, and FIG. 14B shows the
layout of macroblocks after scrambling.
In FIGS. 14A and 14B, first cut points (90, 91) are set in units of
12 consecutive macroblocks in a slice, and second cut points (92,
93, 94, 95) are set in units of four consecutive macroblocks.
Macroblocks are randomly replaced in the horizontal direction in
units of four consecutive macroblocks divided at the second cut
points in each of regions divided by the first cut points, thus
attaining scrambling. The replacing pattern changes in units of
regions divided at the first cut points.
In the example shown in FIGS. 14A and 14B, macroblocks 1 to 4 are
located at the positions of macroblocks 9 to 12, the positions of
macroblocks 5 to 8 remain the same, and macroblocks 9 to 12 are
located at the positions of macroblocks 1 to 4. Upon replacing
macroblocks, offsets corresponding to replacing amounts are added
to the horizontal components of motion vectors.
When motion vectors indicated by arrows in FIG. 14A are detected
from macroblocks 1, 5, and 9, horizontal offsets each corresponding
to the four macroblock widths are added to or subtracted from
motion vectors after scrambling of macroblocks 9 and 1, as shown in
FIG. 14B. Likewise, an identical offset is added to the horizontal
components of motion vectors of all macroblocks contained in each
of regions divided at the second cut points.
However, since the difference value between the motion vectors of
neighboring macroblocks is coded, no offset is added to the
difference vector value to be coded except for the head macroblock
in each of regions divided at the second cut points. Hence, the
number of bits of motion vector data of the head macroblock at the
second cut point slightly increases, but other macroblocks suffer
hardly any increases in the number of coded bits of motion vector
data.
Also, an increase in the number of coded bits of motion vector data
due to an increase in maximum value of motion vectors in a frame
can also be suppressed, since the increase in motion vector size is
limited by the width between neighboring first cut points.
FIGS. 15A and 15B show an example of a video scramble method
according to the 10th embodiment of the present invention. In FIGS.
15A and 15B, upon replacing macroblocks in a slice, the maximum
value between neighboring first cut points, and that between
neighboring second cut points are prescribed, first points are set
at random spacings equal to or smaller than that prescribed value,
second cut points are set at random spacings equal to or smaller
than the prescribed value within each of regions divided by the
first cut points, and macroblocks are replaced in units of
consecutive macroblocks divided at the second points in each of the
regions cut at the first cut points. In the example shown in FIGS.
15A and 15B, the maximum value of the width between neighboring
first cut points is set at 12 macroblocks, and that between
neighboring second cut points are set at 6 macroblocks. The first
and second cut points are also changed in units of slices.
In the uppermost slice in a frame, reference numerals 150 and 151
denote first cut points; and 152, 153, 154, and 155 denote second
cut points. In the second uppermost slice, reference numerals 160
and 161 denote first cut points; and 162, 163, 164, and 165 denote
second cut points. The replacing pattern of regions divided at the
second cut points in each of regions divided at the first cut
points is randomly set in units of regions divided at the first cut
points.
With the aforementioned processes, a scramble pattern which can
suppress an increase in motion vector, allows a large number of
combinations, and is robust against unauthorized attacks can be
generated.
FIGS. 16A and 16B show an example of a video scramble method
according to the 11th embodiment of the present invention. In FIGS.
16A and 16B, slice replacing in the vertical direction shown in
FIGS. 12A and 12B or FIG. 13 is done in addition to macroblock
replacing in the horizontal direction shown in FIGS. 15A and
15B.
In this manner, by combining the scramble method which is
implemented by replacement of macroblocks in the horizontal
direction, and can suppress coding efficiency drop, and the
scramble method which is implemented by replacement of slices in
the vertical direction, an effect of making a picture be hard to
recognize by scrambling can be improved with hardly any
deterioration of image quality of the reconstructed picture. Also,
since the number of combinations of scramble patterns can be
further increased, resilience against unauthorized attacks can be
improved.
To restate, according to the present invention, a frame which is
not used as a reference picture at the coding side is selected, and
is scrambled by replacing pixels in units of slices within a
predetermined vertical range or in units of n consecutive
macroblocks. In this manner, intraframe correlation and interframe
correlation used in coding are prevented from being lost, and any
increase in the number of coded bits of motion vector data can be
suppressed. As a result, a video signal can be scrambled without
any drop of coding efficiency. On the other hand, since a video
signal obtained by decoding is descrambled at the decoding side, a
normal picture can be played back.
Therefore, when the video scramble apparatus according to the
present invention is used, a more robust unauthorized duplication
prevention system and a safer video billing system can be
implemented without any deterioration of image quality in a video
transmission system using coding such as MPEG2 or the like.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
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